The only way you can block this type of call and others is with a call blocker that I have talked about in other posts. I have one and it blocks all unavailable and unknown numbers automatically, it also block up to 80 numbers not like the 12 that Comcast does.
Its $100, and worth it! You can check on Amazon for the Digitone Call Blocker, or you can find other ones that you use your computer if you leave it on all the time.
Good luck.